Effects of Antarctic Bottom Water Formation and Transport on the Distribution and Seasonal Variability of Anthropogenic Carbon
Haoyu Yu, Zhaoru Zhang*, Enhui Liao, Zhangxian Ouyang
The Southern Ocean is the strongest regional sink for anthropogenic carbon (Cant), accounting for approximately 40% of global ocean carbon uptake. Cant is the excess carbon derived from human-emitted atmospheric CO2 that has accumulated in seawater, and its distribution reflects the ocean’s role in buffering climate change. In Antarctic coastal polynyas, sea-ice formation and associated brine rejection generate dense shelf water (DSW), which contributes to Antarctic Bottom Water (AABW) formation and provides a pathway for transporting Cant from Antarctic continental shelves to the deep ocean. Using 10-year numerical simulations from the global coupled physical–biogeochemical model MOM6–COBALTv2, we quantify how DSW formation and transport shape the spatial distributions and seasonal variability of Cant in the Ross Sea, with emphasis on the Drygalski Trough pathway. The results show that Cant is enriched in the Ross Sea DSW source regions and increases with increasing DSW thickness over the continental shelf, whereas this relationship is absent over the continental slope. Along the Drygalski Trough, the seasonal cycle of Cant closely tracks DSW formation in the Terra Nova Bay and its subsequent export toward the continental slope. Particle-tracking experiments further suggest that Cant-rich dense water requires approximately eight months to travel from the Terra Nova Bay to the shelf break. Across the Ross Sea, significant positive correlations between bottom water neutral density and Cant are confined to the major DSW formation regions and export pathways, whereas correlations elsewhere lack a coherent spatial pattern. These results highlight the key role of DSW formation and transport in transporting anthropogenic carbon from the Antarctic continental shelves to the deep ocean.